The invention relates to debris-flushing mechanism in a liquid flow nozzle and, more particularly, to a flushing mechanism for use with nozzles of the constant pressure type, such as utilized in fire fighting.
Fire-fighting nozzles have evolved from simple fixed orifice discharge devices, to adjustable gallonage flow devices, to constant pressure discharge devices, such as exemplified in recent U.S. patents to Allenbaugh, U.S. Pat. No. 4,172,559 and McMillan, U.S. Pat. No. 3,863,844. These improvements in nozzle flow structure and control have been accompanied by advances in discharge pattern control from straight stream to spray and fog, as well as by improved means for flushing entrapped debris from the nozzle outlet, as exemplified in Allenbaugh, U.S. Pat. Nos. 3,012,733 and 3,387,791.
Constant pressure nozzles differ in structure from gallonage or volume controlled nozzles in utilizing a pressure-responsive baffle head which is free to advance or retract in response to fluid supply pressures to the nozzle, thereby varying the discharge outlet or orifice and the discharge volume of fluid to maintain a constant discharge pressure and uniform reach of stream uner changing supply pressure conditions.
Although debris-flushing mechanisms have been available to significantly enlarge the discharge orifice on the controlled gallonage type of nozzle, these flushing mechanisms have not been directly adaptable to constant pressure nozzle structures. Therefore, as evidenced in U.S. Pat. No. 4,172,559, no built-in automatic flushing mechanism has been provided. Instead, for flushing debris from the nozzle, the water flow is shut off and the baffle head is removed or released from its securement to permit flushing when the water is turned on. The water is turned off again to restore the baffle head to its original position and then the nozzle can again be utilized.
It has been found that when existing forms of flushing mechanism are modified to adapt them to constant pressure nozzle structure, hydraulic pressure imbalances are created which interfere with the desitred function of constant pressure discharge in such nozzles.
The problem of flushing debris from a constant pressure nozzle, without the necessity of shutting off the water supply, and without creating the aforementioned hydraulic pressure interference with normal constant pressure function of the nozzle, is the problem to which the present invention is addressed.